Access control systems wherein a passageway normally blocked by gating means, such as a turnstile, is opened upon the insertion of a coin or token into a slot provided for that purpose are well known in the art. In some of the most commonly used systems of this type, the coin or token becomes part of a linkage, whereby the force applied against the blocking turnstile arm by the person seeking to enter the passageway is utilized to unlock the turnstile. Such systems are subject to extremely heavy use, particularly during peak traffic periods. Accordingly, the reliability of such systems and their trouble-free operation for extended periods is a primary concern. Further, since such systems must often operate unattended, they must be capable of withstanding abuse and vandalism with minimum down-time.
As a consequence of the conditions under which they must operate, turnstile systems, particularly those installed in areas of heavy use, have been built as massive devices wherein the use of delicate parts and sensitive adjustments is avoided. As a rule, such a system represents a relatively large capital investment on the part of the private or public operator of the system, e.g. on the part of a transit authority, which is expected to remain in service for an extended period.
The advent of identification recognition systems capable of responding to cards that carry encoded identification indicia, such as magnetic stripes or self-nucleating wires, has added a degree of flexibility not previously available. For example, such cards can be readily adapted to a flexible fare structure, e.g. one that distinguishes between different classes of commuters. Further, by suitably adapting the logic circuitry which receives the signal generated by the card reader, such cards may be encoded to limit their use to certain time periods, e.g. to a particular week or month, or to certain hours of a day. Such cards may also be prepared to provide the user with a specified number of admissions so that, upon the occurrence of each recognition, a cancellation takes place. Following the last one of a predetermined number of cancellations, the card is rejected by the recognition system and no longer unlocks the turnstile.
The adoption of this new technology presents many difficulties with respect to present day access control systems. In many cases, the large investment in existing, operating turnstile systems precludes the substitution of totally new systems. Further, the introduction of the new technology does not as a rule obviate the use of coin-operated turnstile systems, at least for the present. Accordingly, it has been found desirable to retrofit existing turnstile systems in a manner where they are able to accept the newly introduced cards, as well as coins or tokens heretofore in use.
A number of technical problems arise when retrofitting is attempted. In general, a coin successfully passed through the coin receiver, or a card successfully read by the card reader, unlocks the turnstile locking mechanism and permits one individual to pass. In those turnstile systems which are most commonly in use today, wherein the coin temporarily becomes part of the linkage mechanism which acts to unlock the turnstile, the introduction of card readers requires a substitute link which takes the place of the coin. Rather than dropping out of the linkage, as is the case with a coin after the turnstile is unlocked, the substitute link must be retracted from its operative position and held in readiness for subsequent use.
Past attempts at retrofitting such turnstile systems have been largely unsuccessful due to their poor operating reliability. The retrofit construction often results in a condition wherein, due to the relatively large forces involved, the substitute link becomes trapped in its operating position and continues to maintain the turnstile in an unlocked condition after the person has passed through the normally blocked passage.
Repeated failures at devising a reliable retrofit system using the existing mechanism have led to the development of systems wherein the card-operated mechanism of the turnstile is implemented separate and apart from the coin-operated structure. Such turnstile systems have proved to be expensive to build and to maintain owing to the fact that much of the existing structure has to be functionally duplicated. Moreover, the added structure must be accommodated in the limited space available within the turnstile housing, thereby increasing the cost of design, installation and servicing of the turnstile.